The present invention concerns a device and method for checking an aircraft landing gear shock absorber, for example the amount of gas in the landing gear shock absorber and/or the pressure of such gas. More particularly, but not exclusively, this invention concerns a device and method for measuring the pressure in an aircraft landing gear shock absorber and comparing that measurement with an independently made measure in order to ascertain whether an aircraft landing gear shock absorber is filled with the correct amount of gas or not. The invention also concerns a software product for programming a device so that it can perform such a function.
It is desirable for the pressure in aircraft landing gear shock absorbers to be within certain limits. If the pressure within a landing gear shock absorber were to be too low, the shock absorber would be at risk of “bottoming out” during landing, for example, risking damage to the landing gear. If the pressure within a landing gear shock absorber were to be too high, the ability of the shock absorber to dampen peak loading may be reduced. Furthermore, there is a risk of the shock absorber rupturing under the application of a large load (as may be applied if the aircraft is heavily laden and/or on a hard landing). Many landing gear shock absorbers are not fitted with pressure sensors. If pressure sensors are fitted to a landing gear shock absorber, then the pressure sensors are sometimes located in positions which may be difficult to access, for example, close to the fuselage or at the very bottom of the landing gear. As a secondary check to determine pressure, the ground crew typically measure the distance between two parts of the shock absorber. This distance, coupled with knowledge of the aircraft's weight and the ambient temperature, may be used to provide an estimate of the pressure in the shock absorber. This measurement is sometimes known by those skilled in the art as “the H measurement” because it involves measuring the height of one part of the shock absorber in relation to another part. This measurement is prone to significant error, not least because it is difficult to measure the distance between the two parts of the shock absorber with any accuracy. Furthermore, information relating the distance measured to the pressure in the shock absorber is contained on placards which are attached to the landing gear. These placards are often difficult to read, which may make it difficult to determine the pressure from the distance measurement taken. U.S. Pat. No. 6,128,951 discloses the measurement of pressure in landing gear shock absorbers using pressure sensors. U.S. Pat. No. 6,128,951 also discloses the use of a radial variable digital transducer to measure landing gear shock absorber compression and extension.
It is an aim of the present invention to ameliorate one or more of the problems mentioned above. Alternatively or additionally, it is an aim of the present invention to provide an improved or alternative means of assessing the landing gear pressure, which can complement the measurement made with the pressure sensor that measures the landing gear internal pressure.